Arc tube mount



May 26, 1959 E. c.`MARTT E-rvAL 2,888,585

` ARC TUBE MOUNT Filed Aug. so, 195s lrwemfto': Evresfi: C. Marwlrt, Date E. Beemifga,

servator and short-wave ultraviolet filter.

United States Patent ARC TUBE MOUNT Ernest C. Martt, Chagrin Falls, Ohio, yand Dale E.

Beeninga, Milwaukee, Wis., assignors to General Electric Company, a corporation of New York Application August 30, 1956, Serial No. 607,004

7 Claims. (Cl. 313-25) This invention relates to electric lamps of the type having an arc tube mounted in a vitreous outer envelope which keeps air away from arc tube seals and provides mechanical protection while serving also as a heat con- The invention is more particularly concerned with the sealing and with the mounting of the arc tube in the outer envelope or jacket.

High pressure mercury vapor lamps, as known commercially in sizes ranging from 85 to 1000 watts, generally comprise a relatively soft glass outer jacket having a screw base at one end and enclosing a generally cylindrical high pressure arc tube which may be made of hard or quartz-like glass, but is now more commonly of quartz. The arc tube contains a quantity of mercury along with a starting gas and is provided with thermionic electrodes containing a core of material of high electron emissivity. An auxiliary starting electrode -is generally located at one end of the arc tube adjacent one of the main electrodes in order to facilitate starting, and is connected through a current limiting resistor to the main electrode at the opposite end of the arc tube. The space between the ar: tube and the outer bulb may be either evacuated or filled with an inert gas such as nitrogen.

A problem present with such lamps is that of mounting the arc tube within the outer jacket in a manner which is easy and economical to manufacture and which does not interfere with the efficient operation of the arc tube and which preferably absorbs only the very least quantity of light therefrom.

Accordingly an object of the invention is to provide a new and improved seal and mount structure for the arc tube in the outer jacket of a high pressure lamp.

A more specific object is to provide a mounting arrangement for the quartz arc tube in a high pressure vapor lamp which causes minimal absorption of light in the lamp and which is at the same time rugged and economical to manufacture.

In accordance with the invention, the arc tube is closed at its end by pinch seals or presses through which foliatedl leads extend to support the electrodes on their inward projections and in which support wires or dummy leads are fastened which serve as integral mount supports. Preferably four such dummy leads are provided, one in each corner of wide pinch seals utilizing the full diameter of a quartz arc tube at each end, and the arc tube is supported entirely therethrough without the clamps or other fastenings formerly used.

In a preferred construction, the two dummy `leads at the base end of the arc tube, that is the end nearest the stem tube of the outer jacket, are fastened directly to the main inleads therethrough. The dummy leads at the far end of the arc tube either bear directly against the far end of the outer jacket or have fastened thereto suitable spring members which in turn bear against the far end of the jacket. The need for a supporting frame or harp including upright side rods extending parallel the length of the arc tube and which have been major light obstructions, is thus completely eliminated an-d there need be provided but a single flexible lead wire of relatively small size to make electrical connections to the electrode at the far end of the arc tube remote from the base.

For further objects and advantages and for a detailed description of the invention, attention is now directed to the following description and accompanying drawing illustrating embodiments of the invention. The features of the invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawing:

Fig. l is a front elevation View of a high pressure mercury vapor lamp embodying the invention with the front portion of the outer jacket cut away to expose the are tube and its seal and mounting structure.

Fig. 2 is an end View of the lamp of Fig. 1 through section 2-2.

Fig. 3 is a front elevation view of another high pressure mercury vapor lamp forming a preferred embodi ment of the invention.

Fig. 4 is an end view of the lamp of Fig. 3 through section 4 4.

Referring to the drawings and more particularly to Fig. l, there is shown a high pressure mercury vapor lamp l comprising an outer vitreous envelope or jacket 2 of generally tubular form modified by a central bulbous portion 3. The bulbous form reduces the temperature of the envelope in the immediate vicinity of the arc tube where it tends to be highest. The jacket is provided at its lower end with a reentrant stem 4 having a press 5 through which extend relatively stiff inlead wires 6, 7 connected at their outer ends to the contacts of the usual screw type base 8, namely the threaded shell 9 and the insulated center contact 11.

The inner arc tube 12 is made of a highly refractory vitreous material, in the present instance quartz, having sealed therein at opposite ends a pair of main discharge supporting electrodes 1.3, 14 supported on inlead 15, 16 which constitute the arc tube terminals. As illustrated each main electrode comprises a core portion 17 which may be a prolongatio-n of the inner end of thc inlead made of a suitable refractory metal such as tungsten or molybdenum, and surrounded by a tungsten wire helix 18. A small elongated piece or sliver of thorium metal (not shown in the drawing) is inserted between the core and the helix and serves to reduce the cathode drop at the electrodes during operation. An auxiliary starting electrode 21 is provided at the base end of the arc tube adjacent main electrode 13 and supported on an inlead 22.

Current inleads 15, 16 and 22 include intermediate foil sections 23 of molybdenum hermetically united with quartz pinch seal portions 24, 25 and having wire portions welded to the ends of the foil sections and projecting inwardly and outwardly of the seal. Alternatively, one piece foliated inleads may be used, made in accordance with the teachings of Patent 2,667,595-Noe1 et al. Ribbon Lead Construction, issued January 26, 1954 and assigned to the assignee of this application. The arc tube has a filling of an ionizable medium consisting of a supply of mercury in suflicient quantity to be completely vaporized with a pressure or" the order of one-half to several atmospheres during operation of the lamp, and in addition a small quantity of a rare gas such as argon at a low pressure, for instance approximately 25 millimeters pressure measured at room temperature, to facilitate starting.

In the illustrated embodiment of the invention, the pinched end portions 24 and 25 of the arc tube form wide seals using the full diameter of the tube. In other words, the pinch seal is made by attening or compressing the ends of the arc tube Without prior necking down to a smaller diameter by the interposition of a smaller diameter vitreous piece, as has generally been the practice heretofore. The width of the pinch seal then corresponds to approximately 1r/2 times the diameter of the arc tube; in practice it is usually less than the figure obtained by this relationship due to slight necking down of the quartz end by surface tension while heated to a plastic temperature during the sealing operation, but is at least as great as the diameter. Thus in a 40G-watt lamp designated H400-E1 wherein the arc tube has an outside diameter of approximately 22 mm. and an inside diameter of approximtely mm., the pinch width may range 25 to 30 mm.

In accordance with the invention there are provided integral mount supports fastened directly to the arc tube for supporting it within the outer jacket. In the illustrated embodiment there are provided stout dummy leads or integral mount supports 26, 27 in the lower seal 24 at the base end of the lamp, and 28, 29 in the upper seal 25 at the outer end of the lamp. The dummy leads do not extend into the interior of the are tube and accordingly a hermetic seal is not necessar; it suices that they be wedged or mechanically locked in place within the pinch. To assist in so doing, the inner ends of the dummy leads are preferably enlarged in a transverse dimension that is, broadened as by attening or pinching. The ends thereby assume a fish-tail form, as illustrated at 30, which serves to key the leads in the quartz. Since the dummy leads are not required to be hermetically Sealed, they need not be foliated and may be made of round wire. They are preferably made of molybdenum but may be made of other suitably refractory metals such as tungsten or tantalum.

It will be observed that the dummy leads 26 to 29 are located near the corners, that is near the outside lateral edges of the pinch seals 24, 25 in which they are embedded. They are thus considerably removed from the immediate vicinity of the leads and the high heat con- -centrations thereabout. This feature, in addition to the advantage of reducing heat losses normally caused by heretofore conventional mountings wherein channels or brackets encompassed or otherwise engaged the seals, also removes the possibility of any current flow from the electrode inleads to the dummy leads through the quartz and resultant electrolysis of the quartz, in cases where good electrical insulation is desirable.

In the embodiment of Fig. l, a harp or hairpin frame comprising upright side rods 31, 32 is provided for mounting the arc tube. The lower bend of the harp is welded at 33 to lead wire 6 projecting from the stem tube of the jacket. The upper ends of rods 3i, 32 are fixed apart by transverse rod member 3d and have fastened thereto spring members 35, 36 which bear against the tubular outer end of the jacket to hold the arc tube assembly in place. As best seen in Fig. 2, the harp is mounted with its plane turned approximately to the plane of the pinch seals of the arc tube. Dummy leads 26-29 have their ends bent over at right angles to the axis of the arc tube and laterally into the plane of the harp, the ends being fastened to the harp as by welding indicated at 37. The arc tube is thus supported from the harp entirely by the dummy leads and without braces or channel members to engage the seals with their vattendant disadvantages.

A heat reflector disc 3S is mounted transversely to the axis of the envelope near the lower end of the harp and is fastened to the harp by tabs 39 spot-welded to side rods 3l, 32. The connection from inlead 1S of main electrode 13 is made to lead wire 7 through a flexible strap 41 insulated by a vitreous sleeve l2 passing through a central aperture 43 in heat disc 38. Flexible strap 44 for auxiliary electrode inlead 22 is similarly insulated by a glass sleeve where it passes through the heat disc and is connected to a current limiting resistor 45 which in turn is connected to the bend of the harp and thereby vto lead wire 6. The connection to inlead 16 of main electrode 14 at the outer end of the arc tube is made to side rod 31 of the harp through exible strap 46, and through the harp to lead wire 6.

In the preferred embodiment of the invention illustrated in Fig. 3, no harp or frame is used. Lamp la is, except as specifically pointed out hereafter, similar to lamp Il of Fig. l and the same numerals denote corresponding parts; where significant modifications have been made, the part number is followed by the letter a. In this lamp, dummy leads or integral support wires 26a-29a project axially without any bends from the seals. Dummy leads 26a and 27a are fastened directly, for instance by welding, to the laterally turned upper ends 6a and 7a of lead wires 6 and 7 respectively, projecting from the stem tube of the jacket. Dummy lead 26a serves also in part as a current conductor through exible strap 48 which connects it to main electrode inlead 15, thereby completing a circuit to lead wire 6. Inlead 16 of main electrode M at the outer end of the arc tube is connected by a long flexible strap or wire 49 to lead Wire end 7a. Current limiting resistor 45 is connected directly from inlead 22 of auxiliary electrode 21 to lead Wire end 7a. Heat reector disc 38 is modified by a slot 50 in the region of lead wire end 7a so as to avoid contact with that lead or the connections thereto and is spot welded to lead wire end 6a. Dummy leads 28a and 29a at the upper end of the arc tube are fastened to transverse brace members 51 (Fig. 4) which are provided with integral spring fingers 52 bearing against the tubular outer end of the jacket.

Lamp 1a, in addition to the advantages resulting from elimination of clamps or other supports for the seals through the use of dummy leads or integral support wires, also has the advantage of eliminating the harp or frame which was an item of cost and also a disadvantage inasmuchras it unavoidably obstructs light from the are tube. Since long, flexible wire 49 does not provide any mechanical support, it may be of relatively light weight. Furthermore it may be bowed away from the arc tube, as illustrated, whereby to subtend a smaller angle at the arc tube and further reduce the amount of light obstructed; additionally it may be silvered, if desired, to the same end.

The operation of pinching off or attening the entire width of the arc tube without tearing the foliated portions 23 of inleads l5, 16 and 21 is a delicate one. The foil portions are quite fragile, being, for instance, 2 to 2.5 mm. wide and 0.0008 inch thick for the specific lamp described. Accordingly, accurate control of the temperature of the arc tube, and of the pinching pressure and speed with which the pinching jaws close is required. The shape of the jaw surfaces is also of importance and it has been found advisable to use jaws shaped to form a seal as described in copending application Serial No. 607,005 of Klaus Gottschalk, led of even date herewith, entitled Quartz Tube Pinch Seal, and assigned to the same assignee as the present invention. The resulting seal is thicker at the center along an axial line than at the lateral edges, and is thinner, that is, more highly compressed, adjacent the arc tube than at the outer end. Preferably the jaws are provided with shallow grooves cut across in axial and transverse directions in order to restrict ow of the plastic quartz thereunder at pinching, resulting in transverse ridges 53 and axial ridges 54 in the surfaces of the seal as illustrated.

While the present invention has been described by reference to specific preferred embodiments of same, the details of construction described are intended as exemplary and not in order to limit the invention thereto except in so far as included in the accompanying claims.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. An electric lamp of the jacketed type comprising an outer envelope enclosing a vitreous tube, said tube having at each end an axially projecting at pinch seal of width at least substantially as great as the diameter of the tube with a lead-in conductor hermetically sealed through its central portion, and support wires projecting axially from the seals near the lateral edges thereof and forming integral mount supports for the tube Within the outer envelope.

2. An electric lamp of the jacketed type comprising an outer envelope enclosing a vitreous tube, said tube having at each end an axially projecting ilat pinch seal of width at least substantially as great as the diameter of the tube and consisting of the collapsed walls of the tube fused together, said seals having lead-in conductors with intermediate foil portions hermetically sealed through their central portions, and .support wires having an end embedded in the seals and projecting axially from the outer ends of the seals near their lateral edges and forming integral mount supports for the tube and providing substantially the entire mechanical support therefor within the outer envelope.

3. A lamp according to claim 2 wherein the ends of said support wires embedded within the seals are enlarged in a transverse dimension for keying same within the seals.

4. An electric discharge lamp of the jacketed highpressure type comprising a vitreous outer envelope enclosing a quartz arc tube, said tube having at each end an axially projecting at pinch seal of width at least substantially as great as the diameter of the arc tube with a lead-in conductor having an intermediate foil portion hermetically sealed through its central portion, dummy leads embedded Within the seals near their lateral edges and projecting axially from their outer ends, and means within the outer envelope engaging the outer ends of the dummy leads to provide therethrough substantially the entire mechanical support for the arc tube.

5. An electric discharge lamp of the jacketed highpressure type comprising a sealed vitreous outer envelope enclosing a vitreous arc tube, said tube having at each end an axially projecting flat pinch seal of width at least substantially as great as the diameter of the arc tube with a lead-in conductor having an intermediate foil portion hermetically sealed through its central portion, and dummy leads embedded within the seals near their lateral edges and projecting axially from their outer ends, a base at one end of the outer envelope, main inleads sealed through the outer envelope and connected to the base, a harp comprising a pair of spaced side rods extending substantially the length of the outer envelope and fastened at one end to one of the main inleads and having supports, at the other end engaging the outer end of the outer envelope, the dummy leads at each end of the arc tube being bent laterally over towards said side rods and `fastened thereto to maintain the arc tube securely mounted in place within the outer envelope.

6. An electric discharge lamp of the jacketed highpressure type comprising a sealed vitreous outer envelope enclosing a vitreous arc tube, said tube having at each end an axially projecting at pinch seal of width at least substantially as great as the diameter of the arc tube with a lead-in conductor having an intermediate foil portion hermetically sealed through its central portion, dummy leads embedded within the seals near their lateral edges and projecting axially from their outer ends, a base at one end of the outer envelope, main inleads sealed through the outer envelope and connected to the base, the dummy leads at one end of the arc tube being fastened to the main inleads, and supports fastened to the dummy leads at the other end of the arc tube and engaging the outer end of the outer envelope to maintain the arc tube securely mounted in place Within the outer envelope.

7. A lamp as in claim 6 provided with a single electrical conductor of relatively light weight joining the leadin at the outer end of the arc tube to one of the main inleads of the outer envelope.

References Cited in the le of this patent UNITED STATES PATENTS 2,671,183 St. Louis et al. Mar. 2, 1954 2,749,461 Hierholzer et al. June 5, 1956 2,749,462 Kenty et al. June 5, 1956 

